1. Field of the Invention
The present invention relates to an omniaxial thrust vector control system having high side force capability for controlling the flight of solid propellant rocket motor propelled tactical missiles, and in particular, for rapidly changing the flight path of such missiles to intercept highly maneuverable targets in a large envelope.
2. Description of the Prior Art
For tactical missiles such as the Agile type, the most efficient means of performing the required mission is to use a boost-sustain solid propellant rocket motor. The boost phase rapidly accelerates the missile to a high velocity, and the sustain phase maintains or slightly increases this velocity. The longer the sustain phase lasts, the greater the range of the missile. For a given amount of propellant, increasing the sustain duration necessitates lowering of the sustain thrust level. The limit is reached when the thrust level multiplied by the sine of the thrust vector angle reaches the minimum side force required to maintain control. Increasing the thrust vector angle permits a lower sustain thrust level, a longer sustain duration, and increased range. Efficiency drops sharply, however, as large angles are approached, due to the rocket motor nozzle forcing the motor working fluid or gases to undergo a change in direction at or near the throat area where the gases have already attained extremely high velocities within the sonic range.
An omniaxial duct forming assembly for deflecting rocket motor gases and thereby effecting thrust vector control is disclosed in U.S. Pat. No. 3,727,843, granted April 17, 1973 to Arthur R. Parilla for "DUCT-FORMING ASSEMBLIES AND VECTOR CONTROL". That patented duct-forming assembly includes an outer annular member and an inner solid member defining a converging annular duct therebetween having an annular throat section of reduced cross-sectional area. The members are rigidly interconnected for rotation as a unit within a housing. The assembly is characterized in that the annular duct remains fixed in geometry as the members are deflected in the housing, and any change of direction of a fluid passing through the duct is caused to occur in advance of the throat in a region where the area is less restricted and the flow is at a velocity in the subsonic range.
A disadvantage of such prior art duct-forming assembly, particularly for use with tactical missiles using boost-sustain motors, is the limited angular deflection that is permissible, the maximum angle of deflection being of the order of twenty degrees (20.degree.) or less. As a result, the side thrust is substantially less than the undisturbed axial thrust. Another disadvantage resides in the requirement for a special and rather complex duct-forming assembly.
In U.S. Pat. No. 3,485,450, granted on Dec. 32, 1969 to Alexander Kurti et al for "PLANETARY GEAR SYSTEM DRIVE MECHANISM", a swivelable exhaust deflection apparatus is disclosed for deflecting a gas stream of a gas turbine engine for powering vertical take-off and landing aircraft, a planetary gear system being provided for uniplanar rotation of a plurality of nozzle segments from a single power drive. U.S. Pat. No. 3,687,374 discloses a similar swivelable jet nozzle, also swivelable in a single plane, that is proposed for aircraft used to provide a vertical take-off and landing capability. While these prior patents describe nozzle structures having relatively rotatable segments, neither discloses a structure having omniaxial capability.